The present invention is related to ground proximity warning systems and methods for rotary wing aircraft such as helicopters, gyrocopters, and tilt rotors.
Ground proximity warning systems, or GPWS, provide aural and visual warnings of conditions when the aircraft is in potentially hazardous proximity to terrain, and/or in a flight condition apparently inappropriate given the aircraft""s position relative to terrain. Earlier generation ground proximity warning systems sensed dangerous approach to terrain by using a radar altimeter to sense height above the ground. The rate at which height above ground changes, is compared with a predefined envelope(s) to determine if a dangerous condition exists. Classic GPWS systems also contain additional alert functions called xe2x80x98modesxe2x80x99 that alert to other potentially hazardous conditions based on flight regime. Examples of GPWS devices are contained in U.S. Pat. Nos. 3,715,718; 3,936,796; 3,958,218; 3,944,968; 3,947,808; 3,947,810; 3,934,221; 3,958,219; 3,925,751; 3,934,222; 4,060,793; 4,030,065; 4,215,334; and 4,319,218.
Later generation GPWS devices, called EGPWS devices or terrain awareness systems (TAWS), include a stored terrain database that compares the position of the aircraft in three dimensional space with the stored terrain information to identify potential conflicts. EGPWS devices may also include all the functionality and modes of the classic GPWS devices. Examples of EGPWS-type devices include U.S. Pat. Nos. 4,646,244; 5,839,080; 5,414,631; 5,448,563; 5,661,486 4,224,669; 6,088,634; 6,092,009; 6,122,570; and 6,138,060.
The above referenced systems have been primarily developed for fixed wing aircraft. Rotary wing aircraft and aircraft capable of hover present unique challenges for ground proximity alerting due to the different flight profiles flown and the unique capabilities of rotary wing aircraft. For example, unlike fixed wing aircraft, rotary wing aircraft can cease all forward motion while still remaining airborne. Rotary wing aircraft can also descend straight down from a hover to land on all sorts of terrain, and need not make a gradual descent and approach to land as in the case of fixed wing aircraft.
U.S. Pat. No. 5,781,126 titled xe2x80x9cGround Proximity Warning System and Methods for Rotary Wing Aircraft;xe2x80x9d U.S. Pat. No. 5,666,110 titled xe2x80x9cHelicopter Enhanced Descent After Take-off Warning for GPWS;xe2x80x9d and U.S. Pat. No. 6,043,759 titled xe2x80x9cAir Ground Logic System and Method for Rotary Wing Aircraft;xe2x80x9d and co-pending application Ser. No. 08/844,116 titled: xe2x80x9cSystems and Methods for Generating Altitude Callouts for Rotary Wing Aircraft,xe2x80x9d each address various issues associated with applying ground proximity warning technology to rotary wing aircraft and are each incorporated herein by reference. These patents are applicable to both conventional and enhanced ground proximity warning designs for use in helicopters, however, these patents address the particularities of modifying various of the xe2x80x9cmodesxe2x80x9d for use in helicopters. Specifically, U.S. Pat. No. 5,781,126 includes a barometric altitude rate detector including a controller for adjusting this rate detector to account for downwash of the rotary wing. U.S. Pat. No. 5,666,110 discloses a descent after take-off protection envelope. U.S. Pat. No. 6,043,759 discloses a logic method and device for determining when the helicopter is in the airborne or ground state which assists with preventing nuisance alarms during helicopter autorotations. Ser. No. 08/844,116 discloses a device and method for generating altitude call outs during helicopter landing operations.
Helicopters and certain other types of rotary wing aircraft often additionally contain a tail rotor and a tail boom which extends far behind and is out of sight of the pilot. Helicopters are also capable of off-airport landings, such as on rooftops, on oil rigs, and on hillsides, for example. The helicopter geometry and operating characteristics combine to present a risk of a tail strike during low altitude operations. A tail strike can result in significant damage to the aircraft. In certain situations, a tail a strike can cause complete loss of control and/or serious injury or death to the aircraft occupants.
The present invention recognizes the problems in ground proximity alerting for rotary wing aircraft such as, for example, helicopters, gyrocopters and tilt rotors when in the rotor mode, hereinafter generically and interchangeably referred to as xe2x80x9chelicopter(s)xe2x80x9d or xe2x80x9crotary wing aircraftxe2x80x9d. In particular, the present invention recognizes that rotary wing aircraft have unique, yet normal operating capabilities including hover and an off-airport and heliport landing capability.
According to one aspect of the present invention, the invention provides a method, apparatus and computer program product for alerting the pilot of a rotary wing aircraft to a potential tail strike hazard. By monitoring various flight parameters, the present invention can detect a possible tail strike hazard and alert the pilot in sufficient time for evasive action to be taken.
According to another aspect of the present invention, the invention monitors the aircraft pitch, pitch rate, and altitude rate to compute a predicted pitch angle. The predicted pitch angle and height above terrain are used to index a warning envelope. When the current flight regime of the aircraft is contained within the envelope boundaries, a potentially hazardous condition exists and a warning is given.
According to yet another aspect of the present invention, the invention may be included as part of a classic ground proximity warning system as described in U.S. Pat. Nos. 5,781,126; 5,666,110; 6,043,759, or as part of an enhanced ground proximity warning system such as described in co-pending U.S. application Ser. No. 09/865,333 (Attorney Docket No. 543-00-011) filed the same day herewith and titled: xe2x80x9cApparatus, Method and Computer Program Product For Helicopter Enhanced Ground Proximity Warning System.xe2x80x9d